118 lines
4.3 KiB
Markdown
118 lines
4.3 KiB
Markdown
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log
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===
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A Rust library providing a lightweight logging *facade*.
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[](https://github.com/rust-lang/log/actions)
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[](https://crates.io/crates/log)
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[](https://docs.rs/log)
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* [`log` documentation](https://docs.rs/log)
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A logging facade provides a single logging API that abstracts over the actual
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logging implementation. Libraries can use the logging API provided by this
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crate, and the consumer of those libraries can choose the logging
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implementation that is most suitable for its use case.
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## Minimum supported `rustc`
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`1.31.0+`
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This version is explicitly tested in CI and may be bumped in any release as needed. Maintaining compatibility with older compilers is a priority though, so the bar for bumping the minimum supported version is set very high. Any changes to the supported minimum version will be called out in the release notes.
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## Usage
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### In libraries
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Libraries should link only to the `log` crate, and use the provided macros to
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log whatever information will be useful to downstream consumers:
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```toml
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[dependencies]
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log = "0.4"
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```
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```rust
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use log::{info, trace, warn};
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pub fn shave_the_yak(yak: &mut Yak) {
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trace!("Commencing yak shaving");
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loop {
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match find_a_razor() {
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Ok(razor) => {
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info!("Razor located: {}", razor);
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yak.shave(razor);
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break;
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}
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Err(err) => {
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warn!("Unable to locate a razor: {}, retrying", err);
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}
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}
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}
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}
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```
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### In executables
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In order to produce log output, executables have to use a logger implementation compatible with the facade.
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There are many available implementations to choose from, here are some of the most popular ones:
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* Simple minimal loggers:
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* [`env_logger`](https://docs.rs/env_logger/*/env_logger/)
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* [`simple_logger`](https://docs.rs/simple_logger/*/simple_logger/)
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* [`simplelog`](https://docs.rs/simplelog/*/simplelog/)
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* [`pretty_env_logger`](https://docs.rs/pretty_env_logger/*/pretty_env_logger/)
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* [`stderrlog`](https://docs.rs/stderrlog/*/stderrlog/)
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* [`flexi_logger`](https://docs.rs/flexi_logger/*/flexi_logger/)
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* Complex configurable frameworks:
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* [`log4rs`](https://docs.rs/log4rs/*/log4rs/)
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* [`fern`](https://docs.rs/fern/*/fern/)
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* Adaptors for other facilities:
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* [`syslog`](https://docs.rs/syslog/*/syslog/)
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* [`systemd-journal-logger`](https://docs.rs/systemd-journal-logger/*/systemd_journal_logger/)
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* [`slog-stdlog`](https://docs.rs/slog-stdlog/*/slog_stdlog/)
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* [`android_log`](https://docs.rs/android_log/*/android_log/)
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* [`win_dbg_logger`](https://docs.rs/win_dbg_logger/*/win_dbg_logger/)
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* [`db_logger`](https://docs.rs/db_logger/*/db_logger/)
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* For WebAssembly binaries:
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* [`console_log`](https://docs.rs/console_log/*/console_log/)
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* For dynamic libraries:
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* You may need to construct [an FFI-safe wrapper over `log`](https://github.com/rust-lang/log/issues/421) to initialize in your libraries.
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* Utilities:
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* [`log_err`](https://docs.rs/log_err/*/log_err/)
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Executables should choose a logger implementation and initialize it early in the
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runtime of the program. Logger implementations will typically include a
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function to do this. Any log messages generated before the logger is
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initialized will be ignored.
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The executable itself may use the `log` crate to log as well.
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## Structured logging
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If you enable the `kv_unstable` feature, you can associate structured data with your log records:
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```rust
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use log::{info, trace, warn, as_serde, as_error};
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pub fn shave_the_yak(yak: &mut Yak) {
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trace!(target = "yak_events", yak = as_serde!(yak); "Commencing yak shaving");
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loop {
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match find_a_razor() {
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Ok(razor) => {
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info!(razor = razor; "Razor located");
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yak.shave(razor);
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break;
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}
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Err(err) => {
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warn!(err = as_error!(err); "Unable to locate a razor, retrying");
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}
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}
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}
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}
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```
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